Implant systems usually entail two types of pillars or prosthetic abutments' stumps to configure the fixed cemented prosthesis:                Straight abutments        Angled abutments        
There are, generally, two types of straight abutments, those configured in one piece or those configured as a two-part piece. One piece abutments have the threaded portion and the emergent or prosthetic piece joined forming one piece.
In two piece abutments there is an hexagonal or an octagonal socket inside the implant, so that the hexagonal or octagonal platform placed in the lower portion of the abutment fits in the hexagonal socket of the implant and thus prevents the rotation of the emergent prosthetic piece. The whole piece is hollow and is internally traversed by a screw that affixes it to the implant (through screw), said screw being the second piece of the abutment.
Angled abutments are only manufactured in two pieces and follow the same principle as the two piece straight abutments.
There is a great diversity of hexagonal head screwdrivers which function is to screw the angled or straight portion to the implant.
On the other hand, an abutment in two pieces, whether straight or angled, will be screwed in a centric manner, which implies it is easy to use. However, with the passing of time and due to the action of grease, the through screw begins to loosen. Vibration caused by mastication forces and the fat contained in foodstuffs that filters through the joint between the implant and the false prosthetic abutment, or prosthetic pillar, or prosthetic implant, also influence the loosening of the through screw.
Another disadvantage of this system is that, although fitting the hexagon of the false prosthetic abutment to the implant outside the patient's mouth is easy, it becomes difficult when the implant is already set in place in the bone and under the gum, since soft tissue gets in the way and the slightest interposition of tissue results in an imperfect fit, obstructing the passage of the through screw, which creates subsequent problems such as the loosening and fracture of the titanium screw.